1. Field of the Invention
The present invention relates to the field of cable assemblies for use with electrical equipment such as submersible pumping systems in petroleum wells. More particularly, the invention relates to a technique for retaining a cable assembly in a conduit during installation, use and servicing.
2. Description of the Related Art
A number of applications exist for electrical cable assemblies deployed within conduits. In submersible pumping systems, for example, cable assemblies extending from the earth's surface convey power to electrical equipment. The powered equipment typically includes electric motors used to drive pumps and other system components, parameter detection and measurement devices, control circuitry, data storage and transfer devices and so on. At the earth's surface the cable assemblies are coupled to power sources, such as generator sets, and to interface circuitry for the data acquisition and control of the submerged components.
In well applications, several techniques may be employed for routing and supporting cable assemblies. Historically, submersible pumping systems have often been deployed by suspending the equipment on high tensile strength cables. Power and data cables, which are generally incapable of supporting their own weight over the considerable depth of most wells, are secured to the suspension cables. In an increasing number of cases, submersible equipment is supported on lengths of coiled tubing that can be rolled, stored and transported on reels. Such arrangements, referred to as "coiled tubing deployed systems," offer considerable advantages in terms of facility of deployment and retrieval. Moreover, cable assemblies coupled to the equipment may be disposed within the coiled tubing in advance of its deployment. Connections to the submersible equipment are completed subsequently, during installation of the equipment in a well, with connections to above-ground equipment typically being made once the equipment is properly positioned in the well.
Various techniques may be employed for installing and supporting cables within conduits such as coiled tubing. For example, one known technique is to draw the cable into the tubing via a wire line of similar tension system. Alternatively, tensile and compressive forces may be applied to the cables to force them through the tubing. To support the cable, anchors may be coupled along the cable that contact interior surfaces of the tubing to transfer the cable weight to the tubing. Once installed, the tubing may be flooded with a relatively high specific gravity fluid which at least partially supports the cable by virtue of buoyant forces resulting from displacement of the fluid.
In coiled tubing deployed systems, difficulties arise in retention of cable assemblies in the coiled tubing during various phases of installation, use and servicing. In general, cables are extended well beyond the ends of the tubing upon initial installation. At the well, connections are made to the powered equipment or to field matable connectors, and the cable is trimmed to fit within the coiled tubing. At an upper end, similar connections are made to the power supply and other circuitry. For subsequent servicing, the above-ground equipment is disconnected from the cable, and the cable may be withdrawn somewhat from the tubing by pulling slack cable or by moderate elastic deformation (i.e. stretching) of the cable.
Both during initial installation and subsequent servicing of coiled tubing deployed pumping systems, a danger exists that the cable will withdraw into the conduit. In particular, residual strain or elongation may be stored in the cable to varying degrees, depending upon the technique used to position the cable in the tubing. Prior to installation at the final site, recoiling of the tubing for transport or storage may cause the cable to relax and reenter the conduit at one or both ends. During servicing, as the cable is disconnected from above-ground equipment, a similar risk of relaxation and withdrawal exists. Moreover, where sufficient space exists between the tubing inner diameter and the cable, the cable may simply drop into the tubing. In either case, once a cable end is lost within the conduit, a time consuming and expensive retrieval operation is required to extract the cable before normal service can be resumed.
There is a need, therefore, for an improved technique for restraining cables within conduits, such as coiled tubing. In particular, there is a need for a cable restraint system that can be readily employed both prior to and during initial installation of powered equipment, as well as during subsequent servicing.